This invention relates generally to the high-speed movement of tape where tension and speed control are critical factors. The particular disclosure of this application is a closed loop, high-speed tape transporter of the type used to duplicate audio signals off of a rapidly moving master tape onto tape at at least one slaved duplicator.
This process is carried out by passing a closed loop of recording tape across a pick-up head where a signal on the loop of tape is conveyed downstream to the slaved duplicator. The loop of tape is conveyed from the pick-up head into a storage bin for accumulation while a trailing length of the loop of tape is passed across the pick-up head. The loop continues endlessly from the bin back across the pick-up head, with each complete passage of the loop across the pick-up head providing a complete replication of the signal from the loop which is conveyed from the pick-up head to the slaved duplicator.
Typically, a relatively large number, such as ten, slaved duplicators are connected to a single tape transporter of the type described above. Hence, each complete passage of the master tape through the transporter results in ten copies being made. Eventually, these copies are loaded into cassettes for use in tape playback devices.
Tape duplicating processes are subject to a number of industry-imposed standards. A world-wide standard cassette playback speed has been set at 17/8 inches per second (ips) 4.76 centimeters per second (cps) for many years. All speeds at which the tape is processed must therefore be referenced in some manner to this standard. Historically, this has required difficult trade-offs between tape processing speed and tape playback quality. As is well known, the higher the recording speed, the greater the fidelity and playback quality which is obtained. At one time, the tape duplicating industry recorded master tapes at 7.5 ips (19 cps), thereby achieving a very high quality standard. However, in an effort to increase efficiency and output, the duplicating industry began duplicating at 64 times normal speed. However, to reproduce at 64 times 7.5 ips (19 cps) would mean a master tape speed of 480 ips (1219 cps). This was found to be impossible to achieve on a commercial basis, since the master tapes very quickly broke or wore out and, in addition, the playback quality of the duplicated tape was very poor. Therefore, in order to maintain the 64 to 1 ratio, the master recording speed was cut in half to 3.75 ips (9.5 cps), thereby permitting a 64 to 1 duplicating ratio at a master tape speed of 240 ips (610 cps). When 3.75 ips (9.5 cps) was adopted as standard master recording speed, this was acceptable because cassette tape and duplicating slaves were not capable of producing quality sufficient to take advantage of higher recording speeds. However, with the advent of new types of tape, improved recording heads, more sophisticated electronics and the development of Dolby HX Pro high frequency headroom extension system, it became clear that recording the master at 3.75 ips (9.5 cps) constituted a strict upper limit on the quality which could be achieved. Repeated attempts to increase the duplicating speed to 480 ips (1219 cps) has resulted in inefficiencies caused by frequent master tape replacement and poor playback quality. Many of these attempts have involved increasing the speed of the tape transporting capstans in an attempt to simply move the master tape more rapidly through the transporter. However, the physical affects of moving a relatively thin tape at ever increasing speeds are not always linear or even predictable. Experience in the design of tape transporting devices has shown that many different variables controlling tape movement must be controlled and improved to achieve operating efficiency combined with high frequency amplitude stability, high frequency phase stability, and an enhanced stereo image on the end product cassette tape.
The invention described in this application permits a master to be recorded at 7.5 ips (19 cps), and duplicated at a 64 to 1 ratio while substantially improving the efficiency of the tape transporter and the quality of the cassette tape.